Tam has a post up on the somewhat goofy terminology statutes use to define explosives. A man in Arkansas set off a car bomb and was charged with use of a "weapon of mass destruction." Same with the Undie-Bomber. No nukes involved in either case.
I'll give you one better. North Carolina defines a litany of things as a "weapon of mass destruction" - including short-barreled rifles and shotguns. It's not a post-9/11 development, either. Here's a pre-9/11 case interpreting the statute on appeal.